Recent advances in automatic article identification technology provide retail and wholesale sales facilities with an improved means for detecting when an article is being shoplifted. One such method, Electronic Article Surveillance (“EAS”), typically includes an EAS detector and EAS devices commonly called labels, tags. markers or transponders. The EAS detector transmits a radio-frequency (“RF”) carrier signal to any EAS device within a certain range of the detector. An active EAS device responds to the carrier signal by generating a response signal of a predetermined frequency, which triggers an alarm when received at the detector. For example, an active magneto-acoustic EAS tag resonates at a predetermined frequency when stimulated by an interrogation signal. When a customer purchases an item that is protected by an active EAS tag, a cashier typically deactivates the tag using a deactivator that produces a magnetic deactivation field that alters the resonant frequency characteristic of the tag so that it no longer resonates at the predetermined frequency. The item may then be removed from the store without triggering an alarm.
Current EAS deactivation systems require an enabling signal to trigger the deactivation sequence. Presently, the primary method used to trigger the deactivation sequence involves the use of an interrogation field. The interrogation field is typically a radio-frequency magnetic field used to detect the presence of an EAS tag. When an EAS tag enters the interrogation field, the magnetic field induces a frequency response signal, or “EAS marker signal,” for circuitry located within the EAS tag. Frequency detectors detect response signals having a resonant frequency within a predetermined range. When the amplitude of the EAS tag response signal is greater than a predetermined threshold, the EAS deactivation sequence is triggered.
In addition to detecting the mere presence of the EAS tag, the deactivator must also know the orientation of the EAS tag in order to assure proper deactivation. In some deactivators, up to three different magnetic fields are employed in the interrogation zone. Each magnetic field is oriented orthogonally to the other fields in order to ensure that the EAS tag signal is detected and to determine its orientation. Additional circuitry may compare the amplitude of the EAS signal detected in response to each field to determine which field is strongest. The coil producing the strongest response is “fired” to deactivate the EAS tag.
The use of an interrogation field to detect EAS tags has several problems. Because the EAS response signal can vary significantly from label to label, it is difficult to determine exactly what the predetermined threshold for triggering the EAS deactivation sequence should be. This variance can cause the deactivation sequence to be triggered when the tag is not in the correct location, thereby causing failures to deactivate (“FTDs”).
Additionally, creating and detecting the magnetic field inside the interrogation area is very expensive, as at least one receiver and one magnetic field generator are required per deactivator. Also, certain materials may not be suitable for constructing antennas that operate at high frequencies, e.g., laminated, silicon steel does not operate well above about 1 or 2 kHz, requiring the use of more expensive materials for the antenna composition. Thus, the EAS tag detection circuitry alone can potentially add up to about 25% of the total cost of the deactivator.
Also, the EAS marker signal provides little certainty as to the orientation of the EAS tag. All that is really known is which coil produces the strongest response. This inaccuracy further contributes to additional problems with FTDs. Therefore, what is needed is a system, method and EAS tag deactivator for detecting EAS tags without the use of a traditional interrogation field.